Styrenic block copolymer compositions to be used for the manufacture of transparent, gel free films

ABSTRACT

A composition to be used for the manufacture of transparent, gelfree films, comprising: a) at least 65 wt % of a styrenic block copolymer, having a molecular structure according to the formula S—(I/B)—S (1) or [S—(I/B)]n X (2), wherein each S independently is a polymer block of predominantly styrene and (I/B) is a substantially random polymer block of predominantly isoprene and butadiene, wherein n is an integer equal to or greater than 2, and wherein X is the residue of a coupling agent, wherein said styrenic block copolymer having a poly(styrene) content in the range of from 28 to 31% by weight, having poly(styrene) blocks S of a true molecular weight in the range of from 10,000 to 15,000, having a true molecular weight of the complete block copolymer in the range of from 110,000 to 160,000 and wherein the diblock S—(I/B) optionally occurs in a content of at most 20 mol %, b) from 5 to 25 wt % of a second thermoplastic resin, c) from 1 to 10 wt % of a plasticizing oil, the sum of the percentages of the components a, b and c being 100%, and all weight percentages being relative to the weight of the complete composition and extruded or cast or blown mono- or multi-layer films prepared from them.

FIELD OF THE INVENTION

The present invention relates to styrenic block copolymer compositionsto be used for the manufacture of transparent, gel free films.

More in particular the invention relates to styrenic block copolymercompositions which comprise a styrenic block copolymer, comprising atleast one central block obtainable by at random copolymerization ofpredominantly isoprene and butadiene, to be used for the manufacture ofmono- or multilayer films for application in the personal hygieneindustry and showing an improved quality.

BACKGROUND OF THE INVENTION

Elastomeric compositions which an be easily extruded into elastic filmshaving low stress relaxation, low hysteresis or permanent set, and highrecoverable energy are known from e.g. U.S. Pat. Nos. 4,663,220;4,789,699; 4,970,259; 5,093,422; 5,705,556.

Processes for making cast extruded films and extrusion blown films haveto meet high requirements as to the viscosity of the composition.

At the same time, applications of these extrudates in personal hygieneare related to stringent requirements on mechanical behaviour, i.e.combination of stiffness (high modulus) and excellent elasticity (goodstress relaxation and low hysteresis and permanent set) is needed.

One of the greatest challenges in this field is still to find a goodbalance between flow/viscosity and the mechanical properties mentionedabove.

It is an object of the present invention to provide compositions, havean improved balance of properties in personal hygiene applications andmore in particular have an improved balance of properties ofcompositions for mono- or multi-layer films, i.e. compositions showing ahigher melt flow rate (MFR) providing softer, transparent films withoutfines/fish eyes/gels, in combination with lower tensile strength andlower modulus and lower set.

SUMMARY OF THE INVENTION

Accordingly a composition is provided which can be used for themanufacture of transparent, gel free films, comprising:

a) at least 65 wt % of a styrenic block copolymer, having a molecularstructure according to the formula S—(I/B)—S (1) or [S—(I/B)]n X (2),wherein each S independently is a polymer block of predominantly styreneand (I/B) is a substantially random polymer block of predominantlyisoprene and butadiene in a mutual weight ratio in the range of from30/70 to 70/30, wherein said polymer block (I/B) has a glass transitiontemperature (Tg) of at most −60° C. (determined according to ASTME-1356-98), wherein n is an integer equal to or greater than 2, andwherein X is the residue of a coupling agent, wherein said styrenicblock copolymer having a poly(styrene) content in the range of from 28to 31% by weight, having poly(styrene) blocks S of a true molecularweight in the range of from 10,000 to 15,000, having an apparentmolecular weight of the complete block copolymer in the range of from110,000 to 160,000 and wherein the diblock S—(I/B) optionally occurs ina content of at most 20 mole %,b) from 5 to 25 wt % of a thermoplastic resin, which is different fromcomponent (a),c) from 1 to 10 wt % of a plasticizing oil, the sum of the percentagesof the components a, b and c being 100%, and all weight percentagesbeing relative to the weight of the complete composition.

It will be appreciated that another aspect of the invention is formed byextruded mono- or multi-layer films and more in particular by cast orblown mono- or multi-layer films for personal hygiene applications,prepared from the hereinbefore specified compositions.

DETAILED DESCRIPTION OF THE INVENTION

Compositions according to the present invention comprise at least 65 wt% of at least one block copolymer of the formulae S—(I/B)—S or[S—(I/B)]n X and are derived from predominantly isoprene and butadiene.

Preferably said compositions comprise said block copolymer in weightproportions of from 70 to 90 wt %.

In preferred compositions, the mutual weight ratio between isoprene andbutadiene in the I/B blocks is in the range of from 40/60 to 60/40 wt %and more preferably from 45/55 to 55/45 wt % and most preferably from48/52 to 52/48 wt %.

With the terms “predominantly styrene” and “predominantly butadiene”respectively, as used throughout the specification, are meant that forthe respective blocks to be prepared, substantially pure styrene ormixtures comprising at least 95 wt % of styrene and minor amounts ofother comonomers can be used, and substantially pure butadiene ormixtures comprising at least 95 wt % of butadiene and minor amounts ofother comonomers, can be used.

The small proportions of other comonomers in the polystyrene blocks canconsist of structurally related comonomers such as alpha-methyl styrene,p-methyl styrene, o-methyl styrene, p-test.butyl styrene, dimethylstyrene and vinyl naphtalene, or butadiene and/or isoprene.

The small proportions of other comonomers in thepoly(isoprene/butadiene) block can consist of styrene and/orstructurally related alkadienes.

However, preferred block coplymers to be applied according to thepresent invention contain blocks of substantially pure styrene andmixtures of substantially pure isoprene and butadiene.

The block copolymer according to the present invention may be branchedor linear and may be a triblock, tetrablock or multiblock.

It has a structure represented by the general formulaeS—(I/B)—S  (1)or[S—(I/B)]nX  (2)wherein each S independently is a polymer block of predominantly styreneand (I/B) is a copolymer block of substantially at randomly polymerizedmixtures of isoprene and butadiene, in a mutual weight ratio in therange of from 40/60 to 60/40 wt % and preferably from 45/55 to 55/45 wt% and more preferably from 48/52 to 52/48 wt %, wherein said (I/B) blockhas a glass transition temperature (Tg) of at most −60° C. andpreferably in the range of from −85 to −75° C. (determined according toASTM E-1356-98), wherein n is an integer equal to or greater than 2, andwherein X is the residue of a coupling agent.

The polymer blocks S have a true molecular weight in the range of from10,000 to 15,000 and preferably from 10,500 to 14,800.

Preferred block copolymers to be used in the compositions of the presentinvention have apparent total molecular weights in the range of from115,000 to 155,000.

The poly(styrene) content (PSC) in said block copolymers is in the rangeof from 28 to 31 wt % and preferably from 29 to 30 wt %.

The block copolymers to be used according to the present inventionpreferably contain 1,2-vinyl bonds and/or 3,4 vinyl bonds in aproportion of at most 15 wt %, based on the weight of conjugated dieneand preferably of at most 10 wt %.

The block copolymers according the present invention preferably have astorage modulus (g1) of from 1 to 10 MPa in a viscoelasticitymeasurement, in a temperature (7) range of from 0 to 50° C., and onlyone peak on loss tangent (tan 8) attributable to the mixedisoprene/butadiene polymer block at a temperature of −55° C. or below.

With the term “substantially at random polymerized mixtures of isopreneand butadiene” is actually meant that the central (I/B) blocks onlycontain average homopolymer block lengths of less than 100 monomer unitsand preferably of less than 50 monomer units and more preferably of lessthan 20 monomer units.

Said average homopolymer block length may be determined by variousmethods.

The method used in the present application is based on carbon-13 NMR andsaid method has been disclosed in detail in WO 02/057386A, pages 12, 13,14 and 15.

The block copolymers according to the present invention can be preparedby full sequential polymerization of predetermined batches ofpredominantly styrene monomer, of isoprene/butadiene mixtures and ofpredominantly styrene respectively (for triblock copolymers S—(I/B)—S)by anionic polymerization in an inert organic solvent, or by coupling ofan initially prepared living diblock copolymer, obtained by sequentialpolymerization of predetermined batches of predominantly styrene and ofpredominantly isoprene/butadiene by anionic polymerization in an inertorganic solvent, with a coupling agent (to provide triblock ormultiblock copolymers).

In both preparation methods the remaining living block copolymers haveto be terminated by addition of a proton donating agent, such as analkanol, e.g. ethanol or water.

It will be appreciated that block copolymers, prepared by means ofcoupling of living diblock copolymers by means of a coupling agent andtermination of remaining living block copolymers, will finally containsmall amounts (i.e. less than 20 mole % and preferably less than 15 mole% and more preferably less than 10 mole %) of diblock copolymer, havingthe same S blocks (mole % relative to the weight of the total blockcopolymer).

As examples of the coupling agent may be mentioned tin coupling agentssuch as tin dichloride, monomethyltin dichloride, dimethyltindichloride, monoethyltin dichloride, diethyltin dichloride, methyltintrichloride, monobutyltin dichloride, dibutyltin dibromide, monohexyltindichloride and tin tetrachloride; halogenated silicon coupling agentssuch as dichlorosilane, monomethyldichlorosilane,dimethyldichlorosilane, diethyldichlorosilane, monobutyldichlorosilane,dibutyldichlorosilane, monohexyldichlorosilane, dihexyldichlorosilane,dibromosilane, monomethyldibromosilane, dimethyldibromosilane, silicontetrachloride and silicon tetrabromide; alkoxysilanes such astetramethoxysilane; divinyl aromatic compounds such as divinylbenzene endivinyl naphthalene; halogenated alkanes such as dichloroethane,dibromoethane, methylene chloride dibromomethane, dichloropropane,dibromopropane, chloroform, trichloroethane, trichloropropane andtribromopropane; halogenated aromatic compounds such as dibromobenzene;epoxy compounds such as the diglycidyl ether of bisphenol-A (e.g. EPON825 or EPON 826, a trademark), and other coupling agents such as benzoicesters, CO2, 2-chloroprene and 1-chloro-1,3-butadiene and diethyladipateor dimethyladipate.

Of these EPON 825, diglycidyl ethers, dibromobenzene, tetramethoxysilaneand dimethyldichlorosilane are preferred.

The apparent molecular weights of the complete block copolymers and eachof the intermediate precursors have been determined by Gel PermeationChromatography, and expressed in terms of standard poly(styrene), byusing the method described:—ASTM D 3536.

In general, the polymers useful in this invention may be prepared bycontacting the monomer or monomers with an organoalkali metal compoundin a suitable solvent at a temperature within the range from −150° C. to300° C., preferably at a temperature within the range from 0° C. to 100°C. Particularly effective polymerization initiators are organolithiumcompounds having the general formulaRLiwherein R is an aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic or alkyl-substituted aromatic hydrocarbonradical having from 1 to 20 carbon atoms of which sec.butyl ispreferred.

Suitable solvents include those useful in the solution polymerization ofthe polymer and include aliphatic, cycloaliphatic, alkyl-substitutedcycloaliphatic, aromatic and alkyl-substituted aromatic hydrocarbons,ethers and mixtures thereof. Suitable solvents, then, include aliphatichydrocarbons such as butane, pentane, hexane and heptane, cycloaliphatichydrocarbons such as cyclopentane, cyclohexane and cycloheptane,alkyl-substituted cycloaliphatic hydrocarbons such as methylcyclohexaneand methylcycloheptane, aromatic hydrocarbons such as benzene and thealkyl-substituted hydrocarbons such as toluene and xylene, and etherssuch as tetrahydrofuran, diethylether and di-n-butyl ether. Preferredsolvents are cyclopentane or cyclohexane.

The block copolymers according to the general formulae (1) and (2) canbe made by mere adaptation of common processes used for the preparationof S—B—S type block copolymers and/or S—I—S type block copolymers, usinga mixture of butadiene/isoprene instead. Of importance in thepreparation of the block copolymers according to the present inventionis to avoid homopolymer block formation, to ensure appropriate B/Iratio, and to produce a polymer block wherein the random midblock has aTg of −60° C. or less. This generally rules out the use of randomizers,as for instance used by Kuraray in the production of hydrogenatedstyrene isoprene/butadiene block copolymers (reference is made to U.S.Pat. No. 5,618,882 which is incorporated herein.

It may also be beneficial to adapt the process by adding one or bothcomonomers during the formation of the mixed midblock.

Component (b)

The second different thermoplastic polymer component (b) may be selectedfrom the group of polyolefins, polystyrene resins, coumarone-indeneresins, polyindene resins, poly(methylindene) resins, alfa-methylstyreneresins, polyphenylene resins (and in particularpoly(2,6-dimethyl-1,4-phenylene ether) or mixtures of said resins orcopolymers of styrene and other compatible comonomers such as alphamethyl styrene, methyl styrene, vinyl toluene.

Suitable examples of poly(olefin) resins are poly(ethylene),polypropylene or copolymers of ethylene, propylene, alone or with othercomonomers such as EPDM.

Examples of poly(ethylene are HDPE, LDPE, LLDPE. Ethylene or propylenepolymers prepared with metallocene catalysts can also be used.

Preferred components (b) are polystyrenes, having a high molecularweight (i.e. greater than 30,000) clear poly(styrene), toughenedpoly(styrene) or other poly(styrene) homopolymers or copolymers ofstyrene and other compatible comonomers, such as alpha methyl styrene,methyl styrene, vinyl toluene, or blends of polystyrene andpoly(phenylene) resins.

A more preferred component (b) is PS 144c poly(styrene) resin of BASF.Said polystyrenes provide in the compositions of the present inventionfilms, which are transparent and water-white.

The composition preferably comprises from 8 to 12% w of the seconddifferent polymer, relative to the weight of the complete composition.

Component (c)

Suitable plasticizers include plasticizing oils like low aromaticcontent hydrocarbon oils that are paraffinic or naphthenic in character(carbon aromatic distribution <5%, preferably <2%, more preferably 0% asdetermined according to DIN 51378). Those products are commerciallyavailable from the Royal Dutch/Shell Group of companies, like SHELLFLEX,CATENEX, and ONDINA oils. Other oils include KAYDOL oil from Witco, orTUFFLO oils from Arco or PRIMOL oils from EXXON-MOBIL. Otherplasticizers include compatible liquid tackifying resins like REGALREZR-1018. (SHELLFLEX, CATENEX, ONDINA, KAYDOL, TUFFLO, PRIMOL and REGALREZare trademarks).

Other plasticizers may also be added, like olefin oligomers; lowmolecular weight polymers (<30,000 g/mol) like liquid polybutene, liquidpolyisoprene copolymers, liquid styrene/isoprene copolymers or liquidhydrogenated styrene/conjugated diene copolymers; vegetable oils andtheir derivatives; or paraffin and microcrystalline waxes.

More preferably the plasticizer represents a plasticizing oil selectedfrom paraffinic or naphtenic oils, in an amount of from 4 to 6 wt %,relative to the weight of the complete composition.

Additional Auxiliaries

Other rubber components may be incorporated into the adhesivecompositions according to the present invention. It is also known in theart that various other components can be added to modify the tack, theodor, the color of the present compositions and of the resulting film.Antioxidants and other stabilizing ingredients can also be added toprotect the composition of the present invention from degradationinduced by heat, light and processing or during storage.

Several types of antioxidants can be used, either primary antioxidantslike hindered phenols or secondary antioxidants like phosphitederivatives or blends thereof. Examples of commercially availableantioxidants are IRGANOX 565 from Ciba-Geigy(2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tertiary-butylanilino)-1,3,5-triazine), IRGANOX 1010 from Ciba-Geigy(tetrakis-ethylene-(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamate)methane)and POLYGARD HR from Uniroyal(tris-(2,4-di-tertiary-butyl-phenyl)phosphite). Other antioxidantsdeveloped to protect the gelling of the polybutadiene segments can alsobe use, like the SUMILIZER GS from Sumitomo(2[1-(2-hydroxy-3,5-di-ter-pentylphenyl)ethyl)]-4,6-di-tert-pentylphenylacrylate);SUMILIZER T-PD from Sumitomo(pentaerythrythyltetrakis(3-dodecylthiopropionate)); or mixturesthereof. (IRGANOX, POLYGARD and SUMILIZER are trademarks).

Preparation of the Composition

No particular limitation is imposed on the preparation process of thecompositions according to the present invention for the manufacture offilms.

Therefore, there may be used any process such as a mechanically mixingprocess making use of rolls, a Banbury mixer or a Dalton kneader, ortwin-screw extruder, thereby obtaining an intimate solution of thecomposition aimed at.

Use of the Composition

The composition according to the present invention is used for themanufacture of transparent, gel free and preferably water-white, castextruded or extrusion blown films, the combination of mechanical ofwhich and the viscosity of the composition under processing conditions,has been found to be very attractive.

More in particular the composition shows an improved balance ofproperties of films in personal hygiene applications, i.e. a combinationof higher melt flow rate (MFR) and providing softer transparentwater-white mono- or multi-layer films showing lower tensile strength,low modulus, lower set and no fines/fish eyes/gels.

The present invention will hereinafter be described more specifically byreference to the following examples and comparative examples, howeverwithout restricting its scope to these specific embodiments.

Incidentally, all designations of “parts” and “%” as will be used in thefollowing examples mean parts by weight and wt % unless expressly notedotherwise.

EXAMPLES

Synthesis of block copolymers A and B.

Cyclohexane, styrene, butadiene and isoprene were purified by activatedaluminiumoxide and stored at 4° C. under a nitrogen atmosphere.

Dibromoethane (EDB) was used as coupling agent.

Prior to the synthesis, a monomer mixture of butadiene and isoprene (ata weight/weight ratio given in Table 1) was prepared and stored undernitrogen at 4° C.

An autoclave, equipped with a helical stirrer, was charged withcyclohexane and the content was heated to a temperature in the rangefrom 50 to 60° C.

As initiator sec. BuLi was dosed, immediately followed by styrenemonomer, which was allowed to polymerize to completion. The reactiontemperature was increased to 70° C., at which temperature aisoprene/butadiene monomer mixture (I/B) was dosed and reacted.

The resulting diblock was either coupled with an excess EDB or furtherreacted with an additional batch of styrene monomer (full sequentialpolymerization for S—(I/B)—S triblock copolymer).

The excess of coupling agent was optionally scavenged with sec-BuLi andfollowed by addition of ethanol as terminator, or the living triblockcopolymer was terminated by addition of ethanol

The reaction mixture was cooled to 40° C., transported to a blendingvessel and a stabilization package was added (comprising IRGANOX 565 andtris{nonylphenol}phosphate 0.08/0.35 phr as a cyclohexane solution) andstirred at ambient temperature.

Dry block copolymer was obtained by steam coagulation finishing,followed by drying in an oven.

The polymer was analyzed by GPC according to the method described inU.S. Pat. Nos. 5,516,824 and 5,499,409, which are herein incorporated byreference. The results of GPC analysis have been listed in Table 1

TABLE 1 Polymer A B Mw poly(styrene) *10³ 14.8 10.9 Mw Total blockcopol*10³ 153 117 Coupling efficiency % 86 Poly(styrene content) 29.5 30.0I/B ratio 50/50 50/50 Vinyl in B wt % 8 8 Vinyl in I wt % 5 5

The average homopolymer block lengths in the (I/B) blocks have beendetermined by 13C NMR, using the method as disclosed in W002/057386.

13C NMR spectra of polymer samples were obtained with a Bruker AMX-500FT spectrometer operating at 125 MHz. Quantitative proton-decoupledspectra were recorded with a 90° 13C excitation pulse and a repetitionrate of 10 s. 10% (w/w) of polymer solutions in CDCl3 were used. Toimprove the relaxation time, 0.1 mol/l chromium acetyl acetonate wasadded. The applied line broadening was 2 Hz. The spectra were referencedsuch that the aliphatic carbons of trans.polybutadiene are at 31.9 ppm.

The polystyrene content was determined by 1H NMR. Glass transitiontemperatures Tg have been determined by Differential ScanningCalorimetry with a temperature sweep of 40° C./min.

The Tg is measured at the onset of the transition. The details of theadditional components used in these specified compositions, have beenlisted in table 2.

Compositions for the preparation of cast films were prepared by mixingthe components as listed in Table 3 in a Werner & Pfleiderer twin-screwextruder, while also the relevant physical properties of thecompositions have been specified in said table 3.

TABLE 2 KRATON ® D is a linear styrene-butadiene-styrene block 1152 EScopolymer with a PSC of 29.5%, a total molecular weight of 122,000 and acoupling efficiency of 83% KRATON ® D is a linearstyrene-isoprene-styrene block 1161 NS copolymer with a PSC of 15%, atotal molecular weight of 220,000 and a coupling efficiency of 81%KRATON ® D a linear styrene-butadiene-styrene block 1102 CS copolymerwith a PSC of 29.5%, a total molecular weight of 127,000 and a couplingefficiency of 84%. BASF PS a homo poly(styrene) polymer 144c PRIMOL ™ isa paraffinic oil 352 IRGANOX ™ is an antioxidant from CIBA-GEIGY 565EPOLENE ™ is a low density poly(ethylene) from C-10 EASTMAN DOWLEX ™ isa linear low density poly(ethylene) SC 2107 from DOW CHEMICAL

TABLE 3 Examples I II III IV V VI VII VIII Blockco- 70 70 85 90 85 90 8590 polymer A Blockco- polymer B KRATON D- 1152ES KRATON D- 1102CS KRATOND- 15 20 1161NS BASF PS 10 10 10 10 144c Epolene 10 10 C-10 Dowlex 10 10SC2107 Primol 5 5 5 5 352 Irganox 1 1 1 1 1 1 1 1 565 MFR (200° 21.7 1214.5 6 23 12.5 11.5 6.5 C./5 kg) Cast film trans- trans- trans- trans-opaque slightly results parent parent parent parent orange opaqueaverage no gels; no gels - no gels - skin orange amount/ best best bestskin size gels mod. 100% 1.22 1.62 1.83 2.79 1.99 2.25 2.22 2.57 (MPa)mod. 200% 1.52 1.87 2.28 3.48 2.10 2.4 2.46 2.87 (MPa) mod. 300% 1.852.22 2.64 4.13 2.25 2.58 2.68 3.24 (MPa) mod. 500% 2.72 3.01 3.43 5.142.51 2.83 3.06 3.86 (MPa) TS (MPa) 5.1 5.4 6.2 9.2 5.1 >8 >8 >14 EB (%)1170 1520 1710 1725 1655 >2000 >2000 >2000 1st 52.5 63.9 55.6 57.2 61.765.3 61.0 62.5 hysteresis (%) 2nd 36.5 44.0 33.8 33.4 34.2 36.7 34.536.3 hysteresis (%) set (%) 5.8 10.7 4.5 4.8 5.7 6.3 5.5 5.7 Examplescomparative examples IX X i ii iii iv Blockcopolymer A Blockcopolymer B85 90 KRATON D-1152ES 70 70 KRATON D-1102CS 70 KRATON D-1161NS 15 15 2020 BASF PS 144c 10 10 10 10 10 10 Epolene C-10 Dowlex SC2107 Primol 3525 5 5 Irganox 565 1 1 1 1 1 1 MFR (200° C./5 kg) 22 12.5 13.5 18 9.511.5 Cast film results transparent transparent transparent transparentsmall yellow small yellow amount gels; many gels; amount gels; littlegels 3rd best worst 2nd best mod. 100% (MPa) 1.75 2.22 1.39 1.68 1.79 2mod. 200% (MPa) 2.28 2.91 1.74 2.06 2.22 2.42 mod. 300% (MPa) 3.05 3.662.14 2.51 2.72 2.91 mod. 500% (MPa) 5.48 6.13 3.2 3.68 3.93 4.19 TS(MPa) 11.7 21.4 6.8 7.5 8.0 11.9 EB (%) 1435 1800 1420 1245 1520 17301st hysteresis (%) 28.4 39.0 51.9 50.1 56.6 54.0 2nd hysteresis (%) 16.019.3 35.8 33.6 39.1 35.0 set (%) 4.3 5.6 7.1 8.0 9.1 8.4 Molecularparameters Midblock Step I MW PSC CE Coupled Blockcopolymer A 50/50 B/I14.8 153 29.5  86 Full Blookcopolymer B 50/50 B/I 10.9 117 30 100SequentialTest Methods

Melt flow rate (MFR): ASTM D 1238-95 (230° C., 2.16 kg)

Tensile properties according to ASTM D 882-81 (tested on films

Hysteresis: films are elongated to 80% extension at a speed of 100mm/sec (load step) held for 30 sec. and then relaxed to zero force(unload step). A second cycle follows right after the first one.Hysteresis is measured as the difference in energy between the load andunload step. Permanent set is measured as the difference between theoriginal sample length of the first cycle (force equals zero) and thesample length before the second cycle (force equals zero).

It will be appreciated from the results in Table 4 that the use of theblock copolymers A and B (S—(I/B)—S) in compositions I—X, provides animproved processing stability, an improved film quality and at leastequal mechanical properties, as compared to compositions, comprisingblends of SBS and SIS block copolymers.

1. A composition to be used for the manufacture of transparent, gel-freefilms, comprising: a) at least 65 wt % of a styrenic block copolymer,having a molecular structure according to the formulaS—(I/B)—S  (1)or[S—(I/B)]nX  (2), wherein each S independently is a polymer block ofpredominantly styrene and (I/B) is a substantially random polymer blockof predominantly isoprene and butadiene in a mutual weight ratio in therange of from 30/70 to 70/30, wherein said polymer block (I/B) has aglass transition temperature (Tg) of at most −60° C. (determinedaccording to ASTM E-1356-98), wherein n is an integer equal to orgreater than 2, and wherein X is the residue of a coupling agent,wherein said styrenic block copolymer having a poly(styrene) content inthe range of from 28 to 31% by weight, having poly(styrene) blocks S ofa true molecular weight in the range of from 10,000 to 15,000, having anapparent molecular weight of the complete block copolymer in the rangeof from 110,000 to 160,000 and wherein the diblock S—(I/B) optionallyoccurs in a content of at most 20 mol %, b) from 5 to 25 wt % of asecond thermoplastic resin selected from poly(styrene), polyethylene,polypropylene or copolymers of ethylene and propylene, c) from 0 to 10wt % of a plasticizing oil, the sum of the percentages of the componentsa, b and c being 100%, and all weight percentages being relative to theweight of the complete composition.
 2. The composition of claim 1,wherein the component (a) occurs in a weight proportion of from 70 to 90wt %.
 3. The composition of claim 1, wherein polymer block (I/B) hasaverage homopolymer block length PB, respectively PI of less than 100monomer units.
 4. The composition of claim 2 wherein polymer block (I/B)has average homopolymer block length PB, respectively PI of less than 50monomer units.
 5. The composition of claim 3, wherein the mutual weightratio between isoprene and butadiene is in the range of from 48/52 to52/48.
 6. The composition of claim 1, wherein component (b) occurs in aweight proportion of from 8 to 12 wt %.
 7. The composition of claim 1,wherein the component (c) occurs in a weight proportion of from 1 to 10wt %.
 8. The composition of claim 1, wherein the component (c) occurs ina weight proportion of from 4 to 6 wt %.
 9. The composition of claim 1,wherein the component (a) comprises poly(styrene) blocks S, having atrue molecular weight in the range of from 10,500 to 15,000, and saidblock copolymer has an apparent molecular weight of from 115,000 to155,000, and has a poly(styrene) content of from 29 to 30%, and has adiblock S—(I/B) content of from 0 to 15 mole %.
 10. The composition ofclaim 1, wherein i. said component (a) comprises poly(styrene) blocks S,having a true molecular weight in the range of from 10,500 to 15,000,ii. said block copolymer has an apparent molecular weight of from115,000 to 155,000, a poly(styrene) content of from 29 to 30%, and adiblock S—(I/B) content of from 0 to 15 mole %, iii. said component (a)occurs in a weight proportion of from 70 to 90 wt %, said component (b)occurs in a weight proportion of from 8 to 12 wt %, and said component(c) occurs in a weight proportion of from 4 to 6 wt % and iv. saidpolymer block (I/B) has an average homopolymer block length PB,respectively PI of less than 100 monomer units.
 11. A composition to beused for the manufacture of transparent, gel-free films, comprising: a)at least 65 wt % of a styrenic block copolymer, having a molecularstructure according to the formula [S—(I/B)]nX, wherein each Sindependently is a polymer block of predominantly styrene and (I/B) is asubstantially random polymer block of predominantly isoprene andbutadiene in a mutual weight ratio in the range of from 30/70 to 70/30,wherein said polymer block (I/B) has a glass transition temperature (Tg)of at most −60° C. (determined according to ASTM E-1356-98), wherein nis an integer equal to or greater than 2, and wherein X is the residueof a coupling agent, wherein said styrenic block copolymer having apoly(styrene) content in the range of from 28 to 31% by weight, havingpoly(styrene) blocks S of a true molecular weight in the range of from10,000 to 15,000, having an apparent molecular weight of the completeblock copolymer in the range of from 110,000 to 160,000 and wherein thediblock S—(I/B) optionally occurs in a content of at most 20 mol %, b)from 5 to 25 wt % of a second thermoplastic resin selected frompoly(styrene), polyethylene, polypropylene or copolymers of ethylene andpropylene, c) from 0 to 10 wt % of a plasticizing oil, the sum of thepercentages of the components a, b and c being 100%, and all weightpercentages being relative to the weight of the complete composition.